Counterfeiting and diversion continue to be a significant problems in the area of consumer goods. Various marking, authenticating, and identifying schemes have been devised to authenticate and/or track the distribution of goods. For example, U.S. Pat. No. 5,289,547 discloses a method for authenticating articles by incorporating into a carrier composition a mixture of at least two photochromic compounds having different characteristics including absorption maxima during an activated state and color. Discriminating between the different characteristics of the photochromic compounds used, enables the method of identification. U.S. Pat. No. 4,767,205 discloses a code identification by use of microparticles of precise size, shape, and color, and by applying such particles in combinations to an item to be marked. The color identifying system disclosed comprises recognizing and identifying with a light microscope the code comprised of the microparticles. Other methods and compositions have been described for authentication, including inks or dyes or paints that impart photoluminescent or ultraviolet properties; and geometric positioning of threads or strips or particles which are either visibly detectable or detectable by x-ray.
There remains a need to enable efficient labeling or encoding of large numbers of items such as sensitive documents, bank cards, credit cards, controlled access cards, currency, fine art, goods wherein the distribution of which is desirably to be controlled by tracking, objects of commercial value, and such other items which are desired to be tracked or identified. Desirably, the compositions and methods would not be easily duplicated.